OPENING OPERATION AND DUTY CYCLE OF POWER CIRCUIT BREAKERS BASIC INFORMATION AND TUTORIALS

How Power Circuit Breaker Operation
Works?

Reaction time and speed of modern
breakers has increased to reach standard interrupting times of 2 to 5
cycles, with 2 to 3 cycles being common at high voltage. Interrupting
time is measured from energizing of the trip coil until the
extinguishing of the arc.

The interrupting time during close-open
operations may exceed the rated imterrupting time by either 1/2 cycle
(for 2 and 3 cycle breakers) or by 1 cycle (for 5 cycle breakers).

The current standard operating duty
cycle consists of the following:

Open – T – Close – Open - 3 min –
Close – Open

T is defined as either 15 s or 0.3 s
depending on whether the circuit breaker is rated for high speed
reclosing; this distinction is important in application.

Even circuit breakers rated for high
speed reclosing must still be allowed a 0.3-s delay to allow for
proper recovery of insulation following the initial fault
interruption.

For additional operations, and/or any
close operation in the duty cycle with a time delay of less than 15s
after an opening operation, the interrupting rating and related
required capabilities of the oil or air magnetic breaker have to be
derated.

All operations within a 15-min period
are considered part of the same duty cycle and a duty cycle shall
have no more than five opening operations.

For guidance on interrupting capability
for reclosing service for oil and air-magnetic breakers manufactured
after 1960 refer to IEEE C37.0106. Circuit breakers manufactured
prior to IEEE C37.7-196010 have different basis of rating.